A silicon carbide (SiC) epitaxial wafer is produced by making an SiC epitaxial layer grow as an SiC active layer (hereinafter, sometimes referred to as “an active epitaxial layer”) by an epitaxial crystal growth on an SiC substrate. For the purposes of reducing defects of the active epitaxial layer and the like, between an SiC substrate and an active epitaxial layer, an SiC epitaxial layer differing in growth conditions from the active epitaxial layer is formed as a buffer layer (for example, see Patent Documents 1, 2).
For the measurement of the layer thickness of an SiC epitaxial layer, for example, a reflection interference analysis method using a Fourier transform infrared spectrophotometer (Fourier Transform Infrared Spectroscopy; Abbreviation: FT-IR) (hereinafter, sometimes referred to as “an FT-IR method”) is used. Hereinafter, the measurement of the layer thickness of an SiC epitaxial layer by an FT-IR method is sometimes referred to as “the layer thickness measurement by an FT-IR method”.
When there is a refractive index difference greater than or equal to a certain degree between an SiC substrate and an SiC epitaxial layer, the interference of light is generated by light reflected at the surface of the SiC epitaxial layer and light reflected at the interface between the SiC epitaxial layer and the SiC substrate. In the layer thickness measurement by an FT-IR method, by utilizing the interference of light, the layer thickness of the SiC epitaxial layer is derived.